If you pay attention, though, the playground is an excellent place to make scientificobservations and learn more about scientific concepts. Just give it a try. Watch kids swinging on the swings, going up and down on the teeter-totter, and whirling around on the merry-go-round.

Based upon your observations, what conclusions would you make about objects and how they move? What is the natural state of an object? Do objects move by themselves?

Hundreds of years ago, scientists made simple observations just like the ones you can make on the playground. Based upon those observations, they believed that the natural state of an object was to be at rest. It seemed obvious that an outside force had to be applied to make an object move.

For example, the merry-go-round won't simply turn on its own. To enjoy a fun ride, you need to grab the handle and start pushing it in a circle before you jump on and spin around. Eventually, the ride will come to a stop.

Long ago, people believed this simply represented the merry-go-round returning to its natural state of rest. To keep an object moving, they believed that the outside force applied to the object must be continuous. If you're a fan of the merry-go-round, this certainly seems to make sense.

However, one scientist built upon the work of others and made a great intuitiveleap to understand how objects and motion actually work. The scientist? Sir Isaac Newton!

Newton understood that the merry-go-round doesn't come to a stop because it's returning to a natural state of rest. Instead, it comes to a stop because an outside force is acting upon the merry-go-round to stop its motion.

Newton built upon the work of other scientists, including Rene Descartes and Galileo Galilei. Galileo showed that all objects accelerate at the same rate regardless of size or mass. In doing so, he was the first to develop the concept of inertia.

Inertia is the scientificconcept that describes the property of objects with mass to resist changes in their states of motion. You may have heard this concept stated another way: an object at rest tends to stay at rest, and an object in motion tends to stay in motion.

The more inertia an object has, the more mass it has. As a result, the more massive an object is, the more it will resist changes in its state of motion.

Newton stated this principle in his First Law of Motion, which holds that a body at rest will remain at rest and a body in motion will remain motion, unless and until it's acted upon by an outside force. We can observe this principle in action when we see that objects don't start moving, stop moving, or change direction by themselves. They need an outside force acting upon them to do those things.

Going back to the merry-go-round, you can see that a force is required to make it start moving. It would keep moving forever if it weren't for another force — friction — acting to stop its motion.

We must continue to apply force to keep it moving, but not because force is needed to start motion. Instead, the force we must continue to apply to the merry-go-round is necessary to overcome the force of friction that works to stop motion.

Friction is a key force that often works to stop the motion of objects. The more you can reduce friction, the farther an object will move before being stopped.

For example, if you pushed a brick with equal force across concrete and across an ice rink, on which surface would it travel farther? If you said the ice rink, you're correct, because the ice causes much less friction than the concrete.

Did you get it?

Wonder What's Next?

Join us in the Wonderopolis jungle tomorrow as we search for a rare sight!

Try It Out

Are you ready to move? Find a friend or family member to help you explore the following activities:

Need some help visualizing the concept of inertia? Jump online to check out the video and brief explanation at What Is Inertia? Try to explain inertia to a friend or family member in your own words.

Want to test out the concept of inertia for yourself? Ask a friend or family member to help you with one or more of the experiments at Inertia Experiments for Kids online. Have fun testing out this scientific concept at home!

Can you identify examples of inertia in everyday life? Spend some time observing the world around you. Look for objects at rest and in motion. How do they behave? Go for a ride in the car with an adult friend or family member. What happens to your body when the car accelerates and decelerates? Share examples of inertia in everyday life with a friend or family member.

Wonderopolis

Anita Burse

Wonderopolis

Feb 12, 2018

We appreciate your advice! Is there a specific part of this Wonder that you would like to learn more about, Anita? We hope that you take a Wonder Journey to see what else you can discover about Inertia!

Wonderopolis

Molly(Mrs.Thompsans class)

Feb 7, 2018

i really liked learning about inertia because i really like learning new things like math or science and especially things from wonderopolis because it teaches me a lot instead of having to waste teachers time by not knowing what certain things mean.
(WWOTD) it was also made me excited and more energetic when the passage said recess.